Converting CSV To MYSQL With PHP In My Custom Wordpress Plugin

Question

I have a function which converts a file from CSV to MYSQL

The file could be 5,000 rows long up to 90,000 rows long. Based on that I decided in case of problems with uploading the file I would just have the client upload the file with an FTP to a predefined path and then have my program execute that file when the submit button is pressed.

This was in Wordpress but I had a lot of trouble getting this to work with the built in functions. So I wrote my own and got it working. Now I am worried about security and the overall professionalism of my code.

Also I have only tested this with a file that has 5000 rows.

I would like to know if I can do anything to make my program a higher quality and how safe should I feel about larger files coming in based on my code?

<?php
/**
 * Plugin Name: Wuno Uploader
 * Plugin URI: https://www.example.com
 * Description: This plugin adds functionality for uploading CSV files to the database
 * Version: 1.0.0
 * Author: Me
 * Author URI: https://www.example.com
 */

// create custom plugin settings menu
add_action('admin_menu', 'wuno_plugin_create_menu');

function wuno_plugin_create_menu() {

    //create new top-level menu
    add_menu_page('Wuno Plugin Settings', 'Wuno Installer', 'administrator', __FILE__, 'wuno_settings_page' , plugins_url('/images/icon.png', __FILE__) );

    //call register settings function
    add_action( 'admin_init', 'register_wuno_settings' );
}

function register_wuno_settings() {
    //register our settings
    register_setting( 'wuno-settings-group', 'file_to_install' );
    register_setting( 'wuno-settings-group', 'some_other_option' );
    register_setting( 'wuno-settings-group', 'option_etc' );
}  

function productsExec() {
      $hostname='localhost';
      $username='usernmae';
      $password='password';
      $database='db';
      $table_name = "myTable";
      // path where your CSV file is located
      define('CSV_PATH', '../wp-content/plugins/wuno-uploader/');
      // Name of your CSV file
      $csv_file = CSV_PATH . "inventory.csv"; 

      try {
      $dbh = new PDO("mysql:host=$hostname;dbname=$database",$username,$password);
      $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 
      $sql = "DROP TABLE IF EXISTS " . $table_name;
      $dbh->query($sql);

      $sql = "CREATE TABLE IF NOT EXISTS " . $table_name . " (
      id int(8) NOT NULL AUTO_INCREMENT,
      wuno_product varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
      wuno_description varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
      wuno_alternates varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
      wuno_onhand varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
      wuno_condition varchar(255) CHARACTER SET utf8 COLLATE utf8_unicode_ci NOT NULL,
      PRIMARY KEY  (id)
    ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=1 ;"; 
          $dbh->query($sql);

        file_put_contents( $csv_file, preg_replace( "@(\r\n),@", ',', file_get_contents( $csv_file ) ) );
    if (($handle = fopen($csv_file, "r")) !== FALSE) {
           fgetcsv($handle);   
           while (($data = fgetcsv($handle, 0, ",")) !== FALSE) {
                $num = count($data);
                for ($c=0; $c < $num; $c++) {
                  $col[$c] = $data[$c];
                }

         $col1 = $col[0];
         $col2 = $col[1];
         $col3 = $col[2];
         $col4 = $col[3];
         $col5 = $col[4];

        // SQL Query to insert data into DataBase
        $sql = "INSERT INTO " . $table_name . "(wuno_product, wuno_description, wuno_alternates, wuno_onhand, wuno_condition) 
        VALUES('".$col1."','".$col2."','".$col3."','".$col4."','".$col5."')";
        $dbh->query( $sql );
        }
        fclose($handle);
        }
        if ($dbh->query($sql)) {
        echo "<script type= 'text/javascript'>alert('New Record Inserted Successfully');</script>";
        }
        else{
        echo "<script type= 'text/javascript'>alert('Data not successfully Inserted.');</script>";
        }
        $dbh = null;
        }
        catch(PDOException $e)
        {
        echo $e->getMessage();
        }  

 }

function wuno_settings_page() {
 if (isset($_POST['wuno-inventory'])) {
        productsExec();
    } 
?>

<h1>Wuno Inventory Updater</h1>

<form method="POST">
    <label for="wuno-inventory">Path To Inventory</label>
    <input type="text" name="wuno-inventory" id="wuno-inventory" value="inventory.csv">
    <input type="submit" value="Install" class="button button-primary button-large">
</form>

<?php
    }   
?>